AHLs for aviation data over ICAO AFS

Preamble

The WMO Manual on the Global Telecommunication System (WMO-No. 386) was published to facilitate cooperation in respect of meteorological telecommunication between WMO Members and specify obligations in the implementation of the World Weather Watch Global Telecommunication System (GTS).

It provided detailed guidelines for practices and procedures, including abbreviated headers and related specifications, used by the International Civil Aviation Organization (ICAO) for exchanging aeronautical meteorological data through its Aeronautical Fixed Service (AFS). However, according to the WIS 2.0 implementation plan, the Global Telecommunication System (GTS) will be decommissioned by 2033, and National Meteorological and Hydrological Services will use the WIS 2.0 platform for data exchange instead.

At the 78th session of the WMO Executive Council (EC-78), Resolution 16 stated that "the Manual on the Global Telecommunication System (WMO-No.386) will no longer be updated from 31 December 2024” and also requested WMO “…to liaise with ICAO in respect of an extant requirement for Attachment II-5. Data designators T1T2A1A2ii in abbreviated headings of the Manual on the Global Telecommunication System.”

Therefore, this webpage is to ensure the exchange of aviation data over ICAO AFS is not affected by the freezing and subsequent deprecation of WMO-No. 386 and WMO-No. 9 Vol. C1.

Requests for additions or revisions to the abbreviated headings will be managed by the WMO Task Team on Aviation Data based on ICAO requirements.

WMO Abbreviated Headings and Related Specifications Relevant for the Exchange of Aviation Data over ICAO AFS

Version: 1.0.1
Date: 11 August 2025
Location: https://community.wmo.int/en/activity-areas/wis/iwxxm/ahl-icao-data

Abbreviated heading

(Original text from Section 2.3.2, Part II, WMO-No.386)

The abbreviated heading shall have the following format:

T1T2A1A2ii CCCC YYGGgg [BBB]

The symbols shall have the following meanings:

Data designators (T1T2A1A2ii)
- T1T2 - Data type designators.
- A1A2 - Geographical designators.
- ii - It shall be a number with two digits. When an originator or compiler of bulletins issues two or more bulletins with the same T1T2A1A2 and CCCC the ii shall be used to differentiate the bulletins.
Location indicator (CCCC)
- CCCC - International four-letter location indicator of the station or centre originating or compiling the bulletin, as agreed internationally, and published in WMO-No.9, Volume C1, Catalogue of Meteorological Bulletins.
International date-time group (YYGGgg)
- YY - Day of the month
- GGgg - For bulletins containing meteorological reports intended for standard times of observation, the time shall be the standard time of observation in UTC. For aerodrome, route and area (aeronautical) forecasts, it is the standard time of validity.
Modification group (BBB)
- BBB - Shall be added when the abbreviated heading line has already been used for the transmission of a corresponding initial bulletin. Once the initial bulletin has been transmitted, the centre responsible will use the modification group for subsequent, corrected, or amended bulletins as follows:
  1. To transmit information or reports normally contained in an initial bulletin after the initial bulletin has been transmitted or for a subsequent or additional issuance of a bulletin whose abbreviated heading has already been used, the BBB indicator to be used is RRx, where x =:
    - A, for the first bulletin after the issuance of the initial bulletin;
    - B, if another bulletin needs to be issued;
    - and so on up to and including x = X
  2. To transmit a bulletin containing corrected information or reports that have already been issued in a previous bulletin. The BBB indicator to be used is CCx, where x =:
    - A, for the first bulletin containing corrected reports or information;
    - B, if a second bulletin containing corrected reports or information is issued;
    - and so on up to including x = X
  3. To transmit a bulletin containing amendments to the information included in a previously issued bulletin. The BBB indicator to be used is AAx, where x = :
    - A, for the first bulletin containing amendments to information;
    - B, for a second bulletin containing amendments to information;
    - and so on up to and including x = X
  4. If more than 24 BBB indicators have to be used for the sequences detailed in (a), (b) and (c) above, then x = X should continue to be used
  5. For (a), (b) and (c) above, the characters x = Y and x = Z are to be used for special purposes indicated below:
    - x = Y should be used for the encoding of BBB when a system failure causes loss of the record of the sequence of character values assigned to x;
    - x = Z should be used for the encoding of BBB when bulletins are prepared or compiled more than 24 hours after the time of observation.

File naming convention with abbreviated heading

(Original text from Section 4, Attachment II-15, WMO-No.386)

For IWXXM report(s) exchanged as an attachment to an AMHS message over AFS, the file name format shall be as follows:

A_T1T2A1A2iiCCCCYYGGgg[BBB]_C_CCCC_yyyyMMddhhmmss[_ffffff].xml[.compression]

Product identifier (T1T2A1A2iiCCCCYYGGgg): (Same as the abbreviated heading above)
Modification group (BBB): (Same as the modification group above)
Originator (CCCC): (Same as the location indicator above)
Date and time stamp (yyyyMMddhhmmss): Date yyyyMMdd and time hhmmss of creation of the file by the originator.
Free format text (ffffff): (Optional) Six alphanumeric characters containing further identifiers as required by a given originator.
Compression: (Optional) Specifies the compression technique, which if applied should be gz (Unix Gzip) as recommended by ICAO.

Data type designators

Traditional Alphanumeric Code (TAC) messages

(Original text from Tables A and B1, Attachment II-5, WMO-No.386)

T1 Data types
- S - Surface data
- F - Forecasts
- U - Upper-air data
- W - Warnings
- N - Notices

T1	T2	Data type	Code form (name)
S	A	Aviation routine reports	FM 15 (METAR)
S	P	Special aviation weather reports	FM 16 (SPECI)
F	A	Aviation area/GAMET/advisories	FM 53 (ARFOR)/[TEXT]
F	C	Aerodrome (VT < 12 hours)	FM 51 (TAF)
F	T	Aerodrome (VT ≥ 12 hours)	FM 51 (TAF)
F	K	Tropical cyclone advisories	ICAO (Tropical Cyclone Advisory)
F	N	Space weather advisories	ICAO (Space Weather Advisory)
F	V	Volcanic ash advisories	ICAO (Volcanic Ash Advisory)
F	R	Aviation route	FM 54 (ROFOR)
U	A	Aircraft reports	ICAO (AIREP)
W	M	Volcano Observatory Notice for Aviation (VONA)	ICAO (VONA) (new)
W	A	AIRMET	ICAO (AIRMET)
W	S	SIGMET	ICAO (SIGMET)
W	C	Tropical cyclone (SIGMET)	ICAO (SIGMET)
W	V	Volcanic ash clouds (SIGMET)	ICAO (SIGMET)
N	O	METNO	[TEXT]

IWXXM messages

(Original text from Tables A and B7, Attachment II-5, WMO-N0.386)

T1 Data type
- L - Aviation information in XML

T1	T2	Data type	Code form (XML element)
L	A	Aviation routine reports (METAR)	FM 205 (iwxxm:METAR)
L	P	Special aviation weather reports (SPECI)	FM 205 (iwxxm:SPECI)
L	C	Aerodrome forecast (TAF) (VT < 12 hours)	FM 205 (iwxxm:TAF)
L	T	Aerodrome forecast (TAF) (VT ≥ 12 hours)	FM 205 (iwxxm:TAF)
L	K	Tropical cyclone advisories	FM 205(iwxxm:TropicalCycloneAdvisory)
L	N	Space weather advisories	FM 205 (iwxxm:SpaceWeatherAdvisory)
L	U	Volcanic ash advisories	FM 205 (iwxxm:VolcanicAshAdvisory)
L	M	Volcano Observatory Notice for Aviation (VONA)	FM 205 (iwxxm:VolcanoObservatoryNoticeForAviation) (new)
L	W	AIRMET	FM 205 (iwxxm:AIRMET)
L	S	Aviation general warning (SIGMET)	FM 205 (iwxxm:SIGMET)
L	Y	Aviation tropical cyclone warning (SIGMET)	FM 205 (iwxxm:TropicalCycloneSIGMET)
L	V	Aviation volcanic ash warning (SIGMET)	FM 205 (iwxxm:VolcanicAshSIGMET)

Geographical designators

(Original text from Table C1, Attachment II-5, WMO-No. 386)

A1A2.pdf

Location indicator

ICAO Doc 7910 - Location Indicators
or
(Original text from Annex I, WMO-No. 9 Vol. C1)
CCCC.pdf